The brokerage houses don't necessarily matter, but institutions also show up there too.  They do matter.  It's also nice to know how many separate buyers and sellers there are.  If 1 trader or broker is buying or selling a huge amount it could indicate something.  

Anyhow, if you don't care, ignore it.  Other posters do appreciate it.  

Today WZR was kind of boring, the real action was RIM (I know I got a pretty decent trade in).